This invention is directed toward a printer, and more particularly to mechanisms for feeding a recording medium through and for driving a carriage of the printer and to the construction and assembly of a frame to a frame plate of the printer.
A printer typically includes a guiding plate, pressing plate and paper bail for controlling the path of a recording medium such as a sheet of paper as the sheet of paper is advanced through the printer. The sheet of paper is initially inserted against the guiding plate which guides the sheet of paper to a position adjacent a platen. The pressing plate further directs the paper against the platen so as to properly position the paper for printing thereon. The paper bail then presses that portion of the paper which is advanced past the printing head against the platen to properly position the paper for discharge from the printer.
Assembly of the printer requires the guiding plate to be precisely positioned relative to the platen. Otherwise the paper will not be properly fed through the printer. Guiding plates made of polymer materials must be manufactured at a thickness greater than that of other materials such as, but not limited to, metals to maintain the guiding plate in a fixed position during operation of the printer. Due to the greater thickness required, guiding plates made of polymer materials are more expensive to manufacture compared to guiding plates made of metallic materials.
The pressing plate is generally made from metallic materials having relatively high frictional characteristics. Advancing the paper past the pressing plate therefore requires a driving mechanism which produces a relatively high torque. The pressure exerted by the pressing plate is maintained at a fixed level against the platen. Control in the level of pressure exerted by the pressing plate is not possible. Such lack of control is particularly troublesome when a continuous roll of paper is used. The continuous roll of paper has holes along one or both edges thereof and is advanced through the use of a sprocket or tractor. The excessive pressure exerted by the pressing plate against the continuous roll of paper inhibits the advancement of the paper by the sprocket or tractor. Accordingly, the holes in the paper become deformed. Such deformation results in the continuous roll of paper eventually being fed at an unacceptable pitch through the printer.
Operation of the paper bail is also somewhat complicated inasmuch as the bail must be kept from the platen surface until the paper has advanced between the bail and platen. Following discharge of the paper from the printer, the paper bail then must be repositioned away from the platen. In printers having a cut-paper automatic mode of operation, an automatic mechanism for opening and closing the paper bail is required which further complicates the structure of the printer.
Printing mechanisms can be clarified to include a principal scanner portion and a subsidiary scanner portion. The principal scanner portion includes the platen which defines the principal scanner portion and the paper guide. The subsidiary scanner portion includes the motor, carriage, printing head and timing belts and moves the printing head reciprocatably in the lateral direction along the paper (i.e. in directions perpendicular to the direction in which the paper advances).
The carriage on which the printing head is seated is driven in a reciprocating manner by the motor through a timing belt. Positional accuracy of the printing head is obtained by the tension provided from the timing belt. The carriage and timing belt are held in place by a frame plate which is typically made of a metallic material and is generally secured to the frame of the printer by screws to provide the mechanical strength required for reciprocating movement of the carriage and continuous rotation of the timing belt during operation of the printer. Assembly of the frame plate to the frame is often troublesome and time consuming due to the use of screws or the like required for assembly.
The motor employed in the carriage driving mechanism of a conventional printer is also fixed to one end of the frame by screws or the like. The timing belt wraps around the driving pulley which is fixed to a shaft providing the rotational output torque produced by the motor and an additional (i.e. following) pulley which is positioned near the other end of the frame. Consequently, the tension of the timing belt must be controlled by adjusting the torque (i.e. movement) of the motor or the position of the additional pulley.
It is therefore desirable to provide a printer having a guiding plate which need not be assembled within the frame of the printer with the precision demanded from commercially available printers. Guiding plates made from polymer materials should be produced at a cost at least comparable to those made from other suitable materials rather than at a higher cost. It is also desirable to provide a printer whose pressing plate exerts different levels of pressure against the recording medium.
Preferably, use of a paper bail should be avoided to simplify the structure of the printer. Assembly of the frame plate to the frame should be simple and accomplished in relatively little time. The correct tension on the timing belt should be automatically controlled to thereby eliminate the need to manually adjust the movement of the motor or position of a pulley.